针对高分辨率雷达回波信号仿真对带宽、线性度和延时性能的要求, 设计了X波段雷达测试与校准应用的小型化微波光纤延迟线。分析了雷达回波模拟源对距离延迟单元的性能要求, 根据系统指标, 研制了用于宽带雷达信号线性电光转换的关键器件—直接调制分布反馈(DFB)激光器。基于光纤反射镜, 设计与实现了一种小型化的反射式延迟线结构。最后, 利用矢量网络分析仪对系统的微波传输性能进行了测试分析。结果表明: 直接调制DFB激光器的-3dB模拟调制带宽高达21 GHz。基于该激光器的微波光纤延迟线, 针对X波段雷达测试应用可提供40、80、120 μs不同延时的目标回波模拟, 其带内幅度平坦度小于±0.5 dB, 相位非线性小于10°, 同时线性动态范围大于60 dB, 满足雷达回波仿真与校准过程对于信号附加幅频误差和相频误差的要求。

For requirements of a high-resolution radar system for wider bandwidths, higher linearity and longer time delays in the echo simulation, a compact Microwave Fiber Delay Line (MFDL) was designed for measurement and calibration of X-band radars. The performance requirements of a radar echo simulator for the distance delay unit was analyzed. The key component, a directly-modulated Distribution Feedback( DFB) laser, was developed according to the system specifications to implement the linear electro-optic conversion of broadband radar signals. Then, a compact reflective delay line structure was designed and realized based on a fiber mirror. Finally, a vector network analyzer was utilized to measure and analyze the microwave transmission properties of the MFDL. Experimental results indicate that the -3dB analog modulation bandwidth of the DFB laser is up to 21 GHz. The MFDL based on the DFB laser provides the time delays by 40 μs, 80 μs, 120 μs for different targets on typical X-band radar test application, in which the in-band amplitude flatness and phase nonlinearity are less than ±0.5 dB and 10°, respectively, and the system dynamic range is larger than 60 dB. The designed MFDL meets the requirement of radar echo in simulation and calibration for additional amplitude errors and phase errors.